Doors – Use interior door as shed door but under cover

Based on your comment I think what you will need to do is replace the insulation.

As I said in my comment condensation is caused when warm moist air hits a cold surface, be it a window or roof. If your insulation was sound then this would prevent this happening, but it sounds like it letting the air through to the roof.

I'm reluctant to suggest what to replace it with as I haven't seen the roof - so it might be worth getting someone in to quote for the job and ask them what they intend to do.

If you do decide to replace then putting a semi-permeable membrane up as well will help keep the moisture off the cold surfaces.

Almost any door should be hung plumb on both axes, level, and square. Not doing so results in undesirable movement due to gravity along with other adverse functional issues.

In this case, I'd hang the door roughly centered in the opening using shims, then I'd apply casing on the outside to cover the uneven gaps. Optionally case the inside as well. I'd then construct a threshold in an appropriate shape to mate to the door edges and the floor.

The ideal gap between a door jamb and the rough framing is one that's large enough to accommodate out-of-plumb and out-of-level conditions, along with room to shim. More is not helpful, but may also not be a problem if the casing is large enough.

In response to the new information provided... You have a small, lightweight shed. Level the floor by any convenient means and the door opening should return to something approaching plumb/level/square. Then you can hang the door parallel to the opening and expect it to work well.